Process for metallizing plastic surfaces

ABSTRACT

The invention relates to a process for coating plastic surfaces with metals, especially plastic surfaces composed of acrylonitrile/butadiene/styrene copolymers (ABS) and composed of mixtures of these copolymers with other plastics (ABS blends), using an etch solution (composition C) comprising at least one ionic liquid IL, wherein the process comprises the treating of the plastic surface after the etching with an aqueous rinse solution RS while applying ultrasound.

The invention relates to a process for coating plastic surfaces withmetals, especially plastic surfaces composed ofacrylonitrile/butadiene/styrene copolymers (ABS) and composed ofmixtures of these copolymers with other plastics (ABS blends), using anetch solution (composition C) comprising at least one ionic liquid IL,wherein the process comprises the treating of the plastic surface afterthe etching with an aqueous rinse solution RS while applying ultrasound.

The coating of the surfaces of plastic parts with metals, also calledplastic galvanizing, is becoming increasingly important. By plasticgalvanizing methods, composite materials which combine advantages ofplastics and metals are obtained. Plastic can be converted to virtuallyany desired shape by simple processing methods such as injection moldingor extrusion. In addition, the use of plastic components can achieve adistinct reduction in weight in comparison to metal parts. Subsequentgalvanization of the resultant plastic moldings is often conducted fordecorative purposes or else to achieve shielding effects.

For example, sanitary fittings, automobile accessories, furniturehardware, costume jewelry and buttons/knobs are metallized either allover or else only partly, in order to impart an attractive appearance tothe parts. In addition, plastics can also be metallized for functionalreasons. For example, housings of electrical appliances are metallizedin order to shield them from emission or immission of electromagneticradiation. In addition, the surface properties of plastic parts can bealtered in a controlled manner via metallic coatings. In very manycases, copolymers of acrylonitrile, butadiene and styrene (ABScopolymers) and mixtures of these copolymers with other polymers areused, for example blends of ABS and polycarbonate (ABS/PC blends).

For production of metallic coatings on plastic parts, the latter areusually secured in frames and contacted with a plurality of differenttreatment fluids in a particular process sequence. In a first step, forthis purpose, the plastics are typically pretreated in order to removeimpurities such as greases from the surface. Subsequently, etchingmethods are usually used to roughen the surface, such that thesubsequent metal layers adhere with sufficient firmness. In the etchingoperation, the formation of a defined homogeneous structure in the formof recesses on the plastic surface is particularly crucial.

Thereafter, the roughened surface is treated with what are calledactivators in order to form a catalytic surface for a subsequentchemical metallization. For this purpose, it is often the case thateither what are called ionogenic activators or colloidal systems areused. “Kunststoffmetallisierung”, Handbuch für Theorie and Praxis[“Plastic Metallization”, Handbook for Theory and Practice] (Eugen G.Leuze Verlag, Saulgau, 1991, pages 46-47) states, for example, thatplastic surfaces, for activation with ionogenic systems, are firsttreated with tin(II) ions, giving rise to firmly adhering gels of tinoxide hydrate after the treatment and rinsing with water. In thesubsequent treatment with a palladium salt solution, palladium nucleiare formed on the surface through redox reaction with the tin(II)species, these being catalytic for the chemical metallization. Foractivation with colloidal systems, generally colloidal palladiumsolutions are used, formed by reaction of palladium chloride withtin(II) chloride in the presence of excess hydrochloric acid (AnnualBook of ASTM Standard, Vol. 02.05 “Metallic and Inorganic Coatings;Metal Powders, Sintered P/M Structural Parts”, Designation: B727-83,Standard Practice for Preparation of Plastic Materials forElectroplating, 1995, pages 446-450).

After the activation, the plastic parts are typically first chemicallymetallized, using a metastable solution of a metallization bath. Thesebaths generally comprise the metal to be deposited in the form of saltsin an aqueous solution and a reducing agent for the metal salt. Onlywhen the chemical metallization baths come into contact with the metalnuclei on the plastic surface, for example with the palladium seeds, ismetal formed by reduction, which is deposited on the surface as a firmlyadhering layer. Often deposited in the chemical metallization step arecopper, nickel or a nickel alloy with phosphorus and/or boron.

It is then possible to electrolytically deposit further metal layersonto the plastic surfaces coated with the aid of the chemicalmetallization bath. It is often the case that there is first anelectrolytic deposition of copper layers or further nickel layers beforethe desired decorative chromium layer is applied electrochemically.

A critical process step in plastic galvanizing is the pretreatment ofthe plastic surface. One reason why a pretreatment is necessary is toimprove, and typically to actually enable, the adhesion of the metal onthe plastic surface. For this purpose, the plastic surface is roughenedand should obtain more hydrophilic properties. In this context, theformation of a defined homogeneous structure in the form of recesses onthe plastic surface is particularly crucial. These recesses serve, inthe later metallization steps, as the starting point for the growth ofthe metal nuclei.

Since roughening has also been conducted by mechanical methods at anearlier stage, swelling and etching of the plastic surface withchemicals has nowadays become established for this purpose. The mostcommonly used etchant is the chromium-sulfuric acid etchant (chromiumtrioxide in sulfuric acid), especially for ABS(acrylonitrile-butadiene-styrene copolymer) or else polycarbonate.Chromium-sulfuric acid etchant is very toxic and requires specialprecautions in the process procedure, aftertreatment and disposal.Because of chemical processes in the etching process, for example thereduction of the chromium compound used, the chromium-sulfuric acidetchant is used up and is generally not reusable.

A process for chemical metalizing of plastic surfaces using achromium-containing etch solution is described, for example, in DE-A 10054 544.

Also known is the use of ionic liquids for pretreatment (etching) ofplastic surfaces in the context of a metallization. WO 2010/142567describes a process for coating plastics with metal, wherein theplastics are pretreated with a composition comprising at least one salthaving a melting point of less than 100° C. at 1 bar (ionic liquid). Thepretreatment of various thermoplastics is described, for examplepolyamides, polyolefins, polyesters, polyethers, polystyrene andcopolymers of styrene, for example acrylonitrile/butadiene/styrenecopolymer (ABS).

Ionic liquids have been known since the end of the forties. They arefluid salt melts which are liquid below 100° C., preferably at roomtemperature (25° C., 1 bar) and especially at temperatures below roomtemperature. Ionic liquids are a novel class of solvents havingnonmolecular, ionic character.

Typical cation/anion combinations which lead to ionic liquids are, forexample, dialkylimidazolium, pyridinium, ammonium and phosphonium withhalide, tetrafluoroborate, methylsulfate. In addition, there are manyfurther conceivable combinations of cations and anions that lead tolow-melting salts.

The use of ionic liquids in a wide variety of different technical fieldsis known. In connection with polymers, use of ionic liquids as antistatsor else as plasticizers has been described in the prior art, for examplein WO 2004/005391, WO 2007/090755 and WO 2008/006422. Document DE 102009 003 011 discloses the use of ionic liquids as adhesives forpolymers.

It is an object of the present invention to provide an improved processfor coating plastic surfaces with metals, using ionic liquids in thepretreatment of the plastic part. It is possible to dispense with thehitherto customary use of the toxic and disadvantageouschromium-containing etch solutions. An improvement in the coatingprocess may lie firstly in improved strength/adhesion on the plasticsurface and the nature of the metal layer surface, and also in animprovement from a process technology point of view, such as lowerentrainment of the etch solution. The process was to be implementable ina very simple and inexpensive manner, and recovery and/or recycling ofthe etch solution was to be implementable in a very effective manner.

It has been found that, surprisingly, a rinse step using ultrasoundafter the treatment of the plastic surface with the etch solutioncomprising at least one ionic liquid can achieve an improved metalcoating. The ultrasound rinse step of the invention with an aqueousrinse solution can give a homogeneous, shiny, defect-free and verywell-adhering metal surface. More particularly, by means of the processof the invention, it is possible to obtain advantageous metal coatingshaving the layer sequence of chemically deposited nickel, copper,nickel, chromium.

The present invention relates to a process for coating plastic surfaces,especially plastic moldings, with metals, comprising the steps of

-   -   a) pretreating the plastic surface, especially the plastic        molding, with a composition C (etch solution) comprising at        least one ionic liquid IL;    -   b) treating the plastic surface, especially the plastic molding,        from step a) with an aqueous rinse solution RS while applying        ultrasound;    -   c) treating the plastic surface, especially the plastic molding,        from step b) with an activator composition A comprising at least        one ionogenic and/or colloidal activator, especially at least        one palladium component P, preferably at least one colloidal        palladium component P;    -   d) treating the plastic surface, especially the plastic molding,        from step c) with an accelerator composition B comprising an        acid and/or a reducing agent;    -   e) chemically depositing a metal layer, preferably a metal layer        consisting essentially of nickel, copper, chromium or alloys        thereof, by treating the surface from step d) with a coating        composition M1 comprising at least one metal salt, preferably at        least one metal salt selected from nickel, copper and chromium        salts, and at least one reducing agent, preferably an in situ        reducing agent;    -   f) electrochemically coating the surface, especially the plastic        molding, from step e) with at least one further metal layer,        preferably a metal layer consisting essentially of copper and/or        a metal layer consisting essentially of chromium, by        electrochemically treating the surface, especially the plastic        molding, from step e) with at least one coating composition M′        comprising at least one metal compound, especially at least one        metal salt, preferably at least one copper salt, a chromium salt        and/or chromic acid.

Compared to the known use of ionic liquids, it is possible to achieve afurther distinct improvement in the coating outcome, such as betteradhesion of the subsequent metal layers on the plastic surface. It hasbeen found that the ultrasound rinse step can particularlyadvantageously detach partly dissolved plastic particles from thesurface, which leads to more homogeneous structuring of the surface andimproved subsequent metal coating.

A standard definition of ionic liquids delimits them from the known saltmelts by a melting point of below 100° C., preferably below 80° C., orelse even below room temperature. In the context of this application,ionic liquids shall be understood to mean those salts which, in the purestate, have a melting point of less than 100° C. at 1 bar.

It is a feature of the process of the invention that, compared to aconventional rinse step with water, a more homogeneous andbetter-adhering metal coating is obtained. Preferably, all the metallayers, especially the metal layers of the layer sequence of chemicallydeposited nickel, copper, nickel and chromium, have advantageousproperties. In addition, the water consumption in the rinse step can bereduced.

It is additionally advantageous that, in the process of the invention,the plastic surface is etched without metal salts, and it is possible todispense with the use of the toxic and disadvantageouschromium-containing etch solutions.

Plastics and Metals

In the context of the present invention, a molding or a plastic moldingrefers to an article that has originated from a primary forming method,for example an article consisting essentially of plastic that hasoriginated by primary forming methods, for example casting, die casting,injection molding, extrusion blow molding, extrusion, sintering, andoptionally a subsequent forming method. This encompasses especiallyworkpieces and semifinished products, for example a formed workpiece, aninjection-molded workpiece, a film or a foil.

In the process of the invention, plastics, especially plastics having anonconductive surface, are coated with a metal in a plurality of steps.They are preferably thermoplastics. Thermoplastics can be melted andconverted to the desired shape by different methods, for exampleinjection molding, extrusion, thermoforming or blow molding.

Suitable thermoplastics include polyamides, polyolefins, polyesters,polyethers, polyacetals, especially polyoxymethylene, polycarbonates,polyurethanes, polyacrylates, polystyrenes or copolymers of styrene,especially styrene/acrylonitrile copolymers (SAN), acrylicester/styrene/acrylonitrile copolymers (ASA) andacrylonitrile/butadiene/styrene copolymers (ABS).

Polyamides include polycondensates of aminocarboxylic acids, for exampleof 6-aminocarboxylic acid or epsilon-caprolactam, or polycondensates ofdiamino compounds and dicarboxylic acids, for example ofhexane-1,6-diamine and adipic acid.

Suitable polyolefins are polyethylene, polypropylene and copolymers ofethylene or propylene.

Suitable polyesters are polycondensation products of polyhydricalcohols, for example butanediol, hexanediol, glycerol ortrimethylolpropane, and polybasic carboxylic acids, especially phthalicacid and isomers thereof, adipic acid or trimellitic anhydride.

A particular polyacetal is polyoxymethylene (POM).

Polycarbonates are esters of carbonic acid and polyhydric alcohols, forexample bisphenol A; also mentioned are polyestercarbonates comprisingfurther polybasic carboxylic acids as formation components.

Typically, polyethers comprise recurrent ether groups. Of particularindustrial significance are, for example, polyetherimides especiallycomprising aromatic ring systems joined via recurrent ether and imidegroups, polyether ketones especially comprising phenylene groups joinedby recurrent ether and ketone groups, polyether sulfides comprisingether and thioether groups in their polymer backbone, and polyethersulfones comprising recurrent ether groups and sulfone groups in theirpolymer backbone.

Polyurethanes are typical polyadducts formed from polyfunctionalisocyanates and polyhydric alcohols, useful examples being bothaliphatic and aromatic compounds. Polyacrylates are homo- or copolymersof acrylic monomers or methacrylic monomers; a particular example ispolymethylmethacrylate (PMMA).

It is also possible to carry out the process of the invention, whereinthe plastic comprises (or consist of) an carbon-fibre-reinforced epoxyresin. Carbon-fibre-reinforced epoxy resins are commonly known andtypically comprises 10 to 90%, preferably about 50 to 70% by volume,reinforcing carbon-fibre. Suitable epoxy resins are polyethers which areobtained by reaction of an compound having hydroxyl groups, e.g.bisphenol, with an epoxy compound, e.g. epichloro-hydrine. Typically,epoxy resins may be cured by reaction with an hardener, e.g. amines,acids, acid anhydrides, thiols.

Preferred polymers are homo- and copolymers of styrene, such aspolystyrene, styrene/acrylonitrile copolymer and especiallyacrylonitrile/butadiene/styrene copolymers (ABS).

A preferred embodiment relates to the process of the inventiondescribed, wherein the plastic surface is one consisting of orcomprising polyamides, polyolefins, polyesters, polyethers, polyacetals,polycarbonate, polyurethanes, polyacrylates, polystyrene or copolymersof styrene selected from styrene/acrylonitrile copolymers (SAN), acrylicester/styrene/acrylonitrile copolymers (ASA) andacrylonitrile/butadiene/styrene copolymers (ABS). The plastic to becoated may also comprise blends consisting of two or more of theplastics mentioned and/or a plastic part consisting of two or more ofthe plastics mentioned (two-component plastics).

A further preferred embodiment relates to the process of the inventiondescribed, wherein the plastic comprises (or consists of) one or more ofplastics selected from polyamides, polyolefins, polyesters, polyethers,polyacetals, polycarbonate, polyurethanes, polyacrylates, polystyrene orcopolymers of styrene selected from styrene/acrylonitrile copolymers(SAN), acrylic ester/styrene/acrylonitrile copolymers (ASA),acrylonitrile/butadiene/styrene copolymers (ABS) andcarbon-fibre-reinforced epoxy resins.

A preferred embodiment relates to the process of the inventiondescribed, wherein the plastic surface is one consisting of orcomprising polyamides, polystyrenes or copolymers of styrene selectedfrom styrene/acrylonitrile copolymers (SAN), acrylicester/styrene/acrylonitrile copolymers (ASA) andacrylonitrile/butadiene/styrene copolymers (ABS), or blends and/ormulticomponent plastics comprising at least one, preferably at leasttwo, of the plastics mentioned.

Particularly preferred plastics are polyamides and ABS. Most preferably,the plastic comprises acrylonitrile/butadiene/styrene copolymer (ABS) ora blend, for example ABS/PC (acrylonitrile/butadiene/styrene copolymerand polycarbonate) and/or multicomponent plastic comprising ABS. ABS issupplied, for example, under the Terluran® trade name by Styrolution.

The articles to be coated may consist entirely of one or more of theabove plastics. Articles of this kind may have any desired shape and areobtainable, for example, by thermoplastic forming methods such asinjection molding, extrusion, thermoforming and blow molding.Alternatively, they may consist of different materials. What isessential is that the surface to be coated consists of plastic.

In the process of the invention, the plastic or the plastic surface iscoated with metals. Useful metals are especially nickel, aluminium,copper, chromium, tin or zinc and alloys thereof. The metal may beapplied in one or preferably in more than one layer or operation. It ispossible with preference to apply layers of different metals, especiallyat least three different metal layers.

A preferred embodiment relates to the process of the inventiondescribed, wherein the metals comprise at least one metal selected fromnickel, aluminium, copper, chromium, tin, zinc and alloys thereof.

Ionic Liquid IL

The composition C used in the process of the invention comprises atleast one salt having a melting point of less than 100° C. at 1 bar(called ionic liquid IL hereinafter).

Preferably, the ionic liquid IL has a melting point of less than 100°C., more preferably less than 85° C. and most preferably less than 60°C., in each case at 1 bar (standard conditions).

The molar mass of the ionic liquid IL is preferably less than 2000g/mol, more preferably less than 1500 g/mol, more preferably less than1000 g/mol and most preferably less than 750 g/mol; in a particularembodiment, the molar mass is between 100 and 750 g/mol or between 100and 500 g/mol.

Preferred ionic liquids IL comprise at least one organic compound as acation; most preferably, they comprise exclusively organic compounds ascations. Suitable organic cations are especially organic compoundshaving heteroatoms, such as nitrogen, sulfur or phosphorus;

particular preference is given to organic compounds having a cationicgroup selected from an ammonium group, a sulfonium group and aphosphonium group. The ionic liquid IL may especially comprise salts ofthe general formula [A]_(n) ⁺[X]^(n−) where n is 1, 2, 3 or 4, [A]⁺ isan ammonium cation, a sulfonium cation or a phosphonium cation, and [X]⁻is a mono-, di-, tri- or tetravalent anion.

The ionic liquid IL may also comprise mixed salts comprising at leasttwo different organic cations [A]⁺ or mixed salts comprising at leastone organic cation [A]⁺ and one or two different mono-, di-, tri- ortetravalent metal cations [M]^(n+).

In a preferred embodiment, the at least one ionic liquid IL is at leastone salt having a cation selected from imidazolium cations, pyridiniumcations, pyrazolium cations and alkylammonium cations.

In a preferred embodiment, the ionic liquid IL is a combination of atleast one first ionic liquid IL1 and at least one second ionic liquidIL2, the first ionic liquid IL1 comprising, as cation, at least onealkylammonium cation and the second ionic liquid IL2 comprising, ascation, at least one aromatic heterocycle having a delocalized cationiccharge and comprising at least one nitrogen atom. Preferably, thecomposition comprises the at least two different ionic liquids IL1 andIL2 in a mass ratio of IL1 to IL2 in the range from 1 to 20, preferably1.5 to 10, more preferably from 2 to 6, especially preferably from 3 to5, for example 4.

Preferably, the composition comprises the at least two different ionicliquids IL1 and IL2 in a mass ratio of IL1 to IL2 in the range from 1 to20, preferably 3 to 18, more preferably from 5 to 20, especiallypreferably from 7 to 15, for example 7.5 or 15.

Preferably, the ionic liquid IL, especially the ionic liquid IL1,comprises, as cation, at least one, preferably exactly one,alkylammonium cation. In the context of the present invention,alkylammonium cation is understood to mean ammonium compounds having atleast one C₁₋₂₀-alkyl radical, preferably a C₁₋₁₈-alkyl radical, and alocalized positive charge on the nitrogen atom. The compounds may bethose having tetravalent nitrogen (quaternary ammonium compounds) orelse be compounds having trivalent nitrogen, where one bond is a doublebond. Preferably, the alkylammonium cation of the ionic liquid IL1 is anonaromatic compound.

Useful ring systems include monocyclic, bicyclic, nonaromatic ringsystems. Examples include bicyclic systems as described in WO2008/043837. The bicyclic systems of WO 2008/043837 are diazabicycloderivatives, preferably composed of one 7-membered and one 6-memberedring comprising an amidinium group; a particular example is the1,8-diazabicyclo(5.4.0)undec-7-enium cation.

Preferably, the ionic liquid IL, especially the ionic liquid IL1,comprises, as the sole cation, exactly one alkylammonium cation. Theionic liquid IL may alternatively be a mixed salt comprising at leastone alkylammonium cation and at least one further organic cation [A]⁺and/or at least one further metal cation [M]^(n+). Particularlypreferred organic cations are quaternary ammonium cations havingpreferably four C₁₋₁₂-alkyl groups as substituents on the nitrogen atom.

Preference is given to an ionic liquid IL comprising, as cation, atleast one, preferably exactly one, alkylammonium cation of the generalformula (I)

where

-   -   R is an organic group comprising 1 to 20, preferably 1 to 18,        more preferably 1 to 12 and especially preferably 1 to 6 carbon        atoms, where the organic group is a saturated or unsaturated,        acyclic or cyclic aliphatic radical which may be unsubstituted        or may be interrupted or substituted by 1 to 5 heteroatoms or        functional groups;    -   R¹, R² and R³ are each independently:        -   hydrogen;        -   halogen, especially fluorine, chlorine, bromine and iodine,            preferably chlorine;        -   a C₁-C₁₈-alkyl radical which may optionally be substituted            by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo and/or may be interrupted by one or            more oxygen and/or sulfur atoms and/or one or more            substituted or unsubstituted imino groups;        -   a C₂-C₁₈-alkenyl radical which may optionally be substituted            by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo and/or may be interrupted by one or            more oxygen and/or sulfur atoms and/or one or more            substituted or unsubstituted imino groups;        -   a C₅-C₁₂-cycloalkyl radical which may optionally be            substituted by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo;        -   a C₅-C₁₂-cycloalkenyl radical which may optionally be            substituted by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo; or        -   a five- to six-membered heterocycle which includes oxygen,            nitrogen and/or sulfur atoms and may optionally be            substituted by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo,        -   or two adjacent R¹, R² and R³ radicals together with the            nitrogen atom in formula (I) are an unsaturated or saturated            five- to seven-membered ring which may optionally be            substituted by functional groups selected from C₁-C₆-alkyl,            C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen,            amino, cyano and sulfo and may optionally be interrupted by            one or more oxygen and/or sulfur atoms and/or one or more            substituted or unsubstituted imino groups;    -   X is an anion; and    -   n is 1, 2 or 3.

Possible heteroatoms in the definition of the R and R¹ to R³ radicalsare in principle any heteroatoms capable in a formal sense of replacinga —CH₂—, a —CH═, a —C≡ or a ═C═ group. If the carbon-comprising radicalcomprises heteroatoms, preference is given to oxygen, nitrogen, sulfur,phosphorus and silicon. Preferred groups especially include —O—, —S—,—SO—, —SO₂—, —NR′—, —N═, —PR′—, —POR′— and —SiR′₂—, where the R′radicals are the remaining portion of the radical comprising carbonatoms. In cases in which the R¹ to R³ radicals in the abovementionedformulae (I) are bonded to a carbon atom and not to a heteroatom, theycan also be bonded directly via the heteroatom.

Possible functional groups are in principle all functional groups whichcan be bonded to a carbon atom or a heteroatom. Suitable examplesinclude —OH (hydroxyl), ═O (especially in the form of a carbonyl group),—NH₂ (amino), ═NH (imino), —COOH (carboxyl), —CONH₂ (carboxamide), —SO₃H(sulfo) and —CN (cyano). Functional groups and heteroatoms may also bedirectly adjacent, and so combinations of a plurality of adjacent atoms,for instance —O— (ether), —S— (thioether), —COO— (ester), —CONH—(secondary amide) or —CONR′— (tertiary amide), are encompassed as well,for example di(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl orC₁-C₄-alkyloxy.

Halogens are fluorine, chlorine, bromine and iodine.

Preferably, the R radical is

an unbranched or branched C₁-C₂₀-alkyl radical which is unsubstituted ormono- to polysubstituted by hydroxyl, halogen, cyano,C₁-C₆-alkoxycarbonyl and/or sulfo and preferably has a total of 1 to 20carbon atoms, for example methyl, ethyl, 1-propyl, 2-propyl, 1-butyl,2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl),1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl,2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl,2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl,2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, 1-heptyl,1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tetradecyl,1-hexadecyl, 1-octadecyl, 2-hydroxyethyl, 2-cyanoethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(n-butoxycarbonyl)ethyl, 6-hydroxyhexyl and propylsulfo;

glycols, butylene glycols and oligomers thereof having 1 to 100,preferably 1 to 6 and especially preferably 1 to 3 units and a hydrogenor a C₁-C₆-alkyl as end group, for exampleR^(A)O—(CHR^(B)—CH₂—O)_(p)—CHR^(B)—CH₂— orR^(A)O—(CH₂CH₂CH₂CH₂O)_(p)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B) arepreferably hydrogen, methyl or ethyl and p is preferably 0 to 3,especially 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl, 3,6-dioxaoctyl,3,6,9-trioxadecyl, 3,6,9-trioxaundecyl, 3,6,9,12-tetraoxatridecyl and3,6,9,12-tetraoxatetradecyl;

vinyl;

or an unsubstituted C₅-C₁₂-cycloalkenyl radical.

More preferably, the R radical is unbranched and unsubstitutedC₁-C₁₈-alkyl, preferably C₁-C₁₂-alkyl, for example methyl, ethyl,1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, or isCH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— and CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂— with p=0 to3.

Preferably, the R¹, R² and R³ radicals are each independently

-   -   hydrogen;    -   a C₁-C₁₈-alkyl radical which may optionally be mono- to        polysubstituted by functional groups selected from C₁-C₆-alkyl,        C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl, hydroxyl, halogen, amino,        cyano and sulfo, for example methyl, ethyl, 1-propyl, 2-propyl,        1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl),        2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl,        2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl,        3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl,        3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,        4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,        4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,        2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,        3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,        3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl,        1-undecyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl,        2-hydroxyethyl, 2-cyanoethyl, 2-cyanopropyl,        2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,        2-(n-butoxycarbonyl)ethyl, 2-hydroxyethyl, 2-hydroxypropyl,        3-hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl,        2-aminopropyl, 3-aminopropyl, 4-aminobutyl, 6-aminohexyl,        2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl,        4-methylaminobutyl, 6-methylaminohexyl, 2-dimethylaminoethyl,        2-dimethylaminopropyl, 3-dimethylaminopropyl,        4-dimethylaminobutyl, 6-dimethylaminohexyl,        2-hydroxy-2,2-dimethylethyl, 2-methoxyethyl, 2-methoxypropyl,        3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl,        2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl, 6-ethoxyhexyl,        chloromethyl, 2-chloroethyl, trichloromethyl,        1,1-dimethyl-2-chloroethyl, methoxymethyl, 2-butoxyethyl,        diethoxymethyl, diethoxyethyl, 2-isopropoxyethyl,        2-butoxypropyl, 2-octyloxyethyl, 2-methoxyisopropyl and        propylsulfo;    -   a C₅-C₁₂-cycloalkyl radical which may optionally be substituted        by C₁-C₆-alkyl; for example cyclopentyl and cyclohexyl;    -   glycols, butylene glycols and oligomers thereof having 1 to 100,        preferably 1 to 6 and especially preferably 1 to 3 units and a        hydrogen or a C₁-C₆-alkyl as end group, for example        R^(A)O—(CHR^(B)—CH₂—O)_(p)—CHR^(B)—CH₂— or        R^(A)O—(CH₂CH₂CH₂CH₂O)_(p)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B)        are preferably hydrogen, methyl or ethyl and p is preferably 0        to 3, especially 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl,        3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxaundecyl,        3,6,9,12-tetraoxatridecyl, 3,6,9,12-tetraoxatetradecyl,        5-hydroxy-3-oxapentyl, 8-hydroxy-3,6-dioxaoctyl,        11-hydroxy-3,6,9-trioxaundecyl, 7-hydroxy-4-oxaheptyl,        11-hydroxy-4,8-dioxaundecyl, 15-hydroxy-4,8,12-trioxapentadecyl,        9-hydroxy-5-oxanonyl, 14-hydroxy-5,10-dioxatetradecyl,        5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl,        11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl,        11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapentadecyl,        9-methoxy-5-oxanonyl, 14-methoxy-5,10-dioxatetradecyl,        5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl,        11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl,        11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl,        9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl;    -   or two adjacent R¹, R² and R³ radicals together with the        nitrogen atom in formula (I) are a saturated unsubstituted five-        to seven-membered ring; for example, two adjacent R¹, R² and R³        radicals are 1,4-butylene, 1,5-pentylene or 3-oxa-1,5-pentylene.

In one embodiment, two adjacent R¹, R² and R³ radicals together with thenitrogen atom in formula (I) may be an unsaturated or saturated five- toseven-membered ring which may optionally be substituted by functionalgroups selected from C₁-C₆-alkyl, C₁-C₆-alkyloxy, C₁-C₆-alkoxycarbonyl,hydroxyl, halogen, amino, cyano and sulfo and may optionally beinterrupted by one or more oxygen and/or sulfur atoms and/or one or moresubstituted or unsubstituted imino groups. Preferably, two adjacent R¹,R² and R³ radicals together with the nitrogen atom in formula (I) form asaturated five- to seven-membered ring and two adjacent R¹, R² and R³radicals are 1,4-butylene, 1,5-pentylene or 3-oxa-1,5-pentylene.

Most preferably, the R¹, R² and R³ radicals are each independentlyhydrogen, unsubstituted C₁-C₁₈-alkyl, preferably C₁-C₁₂-alkyl (forexample methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl),2-hydroxyethyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl,2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, chlorine,CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂— where p=0 to3 or two adjacent R¹, R² and R³ radicals are 1,4-butylene, 1,5-pentyleneor 3-oxa-1,5-pentylene.

More preferably, R¹, R² and R³ are a hydrogen atom or an above-describedhydrocarbyl group having no further heteroatoms. Most preferably, R¹, R²and R³ are a hydrogen atom or an unsubstituted C₁-C₁₈ alkyl group, morepreferably a C₁-C₆ alkyl group, for example a methyl group, ethyl group,propyl group, isopropyl group or n-butyl group.

More preferably, the at least one ionic liquid IL1 comprises analkylammonium cation of formula (I)

where

-   -   R is an unbranched and unsubstituted C₁-C₁₈-alkyl (for example        methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl,        1-octyl, 1-decyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl,        1-octadecyl, especially methyl, ethyl, 1-butyl and 1-octyl),        CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂— with        p=0 to 3;    -   R¹, R² and R³ are each independently:        -   a hydrogen atom, unsubstituted C₁-C₁₈-alkyl (for example            methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl,            1-octyl), 2-hydroxyethyl, 2-cyanoethyl,            2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,            2-(n-butoxycarbonyl)ethyl, chlorine,            CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂—            with p=0 to 3,        -   or two adjacent R¹, R² and R³ radicals together with the            nitrogen atom in formula (I) are a saturated unsubstituted            five- to seven-membered ring, for example 1,4-butylene,            1,5-pentylene or 3-oxa-1,5-pentylene.    -   X is an anion; and    -   n is 1, 2 or 3.

More preferably, the ionic liquid IL1 comprises an alkylammonium cationof formula (I) where

-   -   R is C₁-C₁₈-alkyl, preferably C₁-C₆-alkyl, and R¹, R² and R³ are        each independently a hydrogen atom or C₁-C₁₈-alkyl, preferably        C₁-C₆-alkyl;    -   or    -   R is C₁-C₁₈-alkyl, preferably C₁-C₆-alkyl; R¹ and R² together        are 1,5-pentylene or 3-oxa-1,5-pentylene and R³ is a hydrogen        atom or C₁-C₁₈-alkyl, preferably C₁-C₆-alkyl.

Most preferred alkylammonium cations in the ionic liquid IL1 aremethyltri(1-butyl)ammonium, 1-butyl-1-methylpyrrolidinium,N,N-dimethylpiperidinium and N,N-dimethylmorpholinium.

Preferred anions, especially preferred X^(n−) anions according toformula (I), are described below.

Especially preferred are ionic liquids IL comprising, as cation,methyltri(1-butyl)ammonium and, as anion, an anion selected fromchloride, bromide, hydrogensulfate, tetrachloroaluminate, thiocyanate,methylsulfate, ethylsulfate, methanesulfonate, formate, acetate,dimethylphosphate, diethylphosphate, p-tolylsulfonate, tetrafluoroborateand hexafluorophosphate.

Especially preferably, the ionic liquids IL1 aremethyltri(1-butyl)ammonium methylsulfate (MTBS) or1-butyl-1-methylpyrrolidinium dimethylphosphate, more preferablymethyltri(1-butyl)ammonium methylsulfate (MTBS).

The alkylammonium cation of the ionic liquid IL may also be aheterocyclic ring system comprising at least one and preferably one ortwo tetra- and/or trivalent nitrogen(s), where one bond is a doublebond. For example, the cation of the ionic liquid IL, especially of theionic liquid id IL1, may be a cyclic nonaromatic alkylammonium cationselected from the group consisting of piperidinium cations, pyrazoliumcations, pyrazolinium cations, imidazolinium cations, pyrrolidiniumcations, imidazolidinium cations, guanidiumium cations and choliniumcations.

Suitable cations of the at least one ionic liquid IL, especially of theionic liquid IL1, are, for example, the cations of the general formulae(IIa) to (IIj)

where R is as defined above and the R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹ andR¹² radicals are each as defined above for the R¹, R² and R³ radicals.

In a preferred embodiment, the composition C may comprise an ionicliquid IL comprising, as cation, at least one aromatic heterocyclehaving a delocalized cationic charge and comprising at least onenitrogen atom, preferably one, two or three nitrogen atoms (alsoreferred to as ionic liquid IL2). More particularly, the at least onenitrogen atom, preferably one, two or three nitrogen atoms, is in thering system of the heterocycle. Preferably, the ionic liquid IL2comprises, as cation, exactly one aromatic heterocycle having adelocalized cationic charge and comprising at least one nitrogen atom.The ionic liquid IL2 may alternatively be a mixed salt comprising atleast one aromatic heterocycle and at least one further organic cation[A]⁺ and/or at least one further metal cation [M]^(n+).

The composition C may comprise the ionic liquid IL2 as the sole ionicliquid or in combination with other ionic liquids, especially incombination with the above-described ionic liquid comprising, as cation,at least one alkylammonium cation (ionic liquid IL1).

Most preferably, the ionic liquid IL comprises, as cation, a five- orsix-membered heterocyclic aromatic ring system having one, two or three,preferably one or two, nitrogen atoms as part of the ring system. Inprinciple, the five- or six-membered heterocyclic aromatic ring systemmay comprise one or two further heteroatoms, especially oxygen and/orsulfur atoms. The carbon atoms of the aromatic ring system may besubstituted by organic groups having generally not more than 20 carbonatoms, preferably by a hydrocarbyl group, especially a C₁-C₁₆ alkylgroup, especially a C₁-C₁₀ and more preferably a C₁-C₄ alkyl group.

Suitable cations of the at least one ionic liquid IL are, for example,the cations of the general formulae (IIk) to (IIs′)

where R is as defined above and the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals areeach as defined above for the R¹, R² and R³ radicals. Preferably, theR⁴, R⁵, R⁶, R⁷ and R⁸ radicals are each independently selected fromhydrogen, methyl, ethyl, 1-propyl, 1-butyl and chlorine.

Preferably, the cation of the at least one ionic liquid IL2 is a cationof the abovementioned formulae (IIk), (IIo), (IIp), (IIq), (IIq) and(IIr), most preferably a cation of the formula (IIo).

Very particular preference is given to ionic liquids IL in which thecation is a pyridinium cation of the formula (IIk) where

-   -   one of the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals is methyl, ethyl or        chlorine and the remaining R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are        hydrogen; or    -   R⁶ is dimethylamino and the remaining R⁴, R⁵, R⁷ and R⁸ radicals        are hydrogen; or    -   all the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen; or    -   R⁵ is carboxyl or carboxamide and the remaining R⁴, R⁶, R⁷ and        R⁸ radicals are hydrogen; or    -   R⁴ and R⁵ or R⁵ and R⁶ are 1,4-buta-1,3-dienylene and the        remaining R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen.

Especially preferred are ionic liquids IL in which the cation is apyridinium cation of the formula (IIk) where

-   -   all the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals are hydrogen; or    -   one of the R⁴, R⁵, R⁶, R⁷ and R⁸ radicals is methyl or ethyl and        the remaining R⁴, R⁵, R⁶,

R⁷ and R⁸ radicals are hydrogen.

Very particularly preferred pyridinium cations (IIk) include1-methylpyridinium, 1-ethylpyridinium, 1-(1-butyl)pyridinium,1-(1-octyl)pyridinium, 1-(1-hexyl)pyridinium,1-(1-octyl)pyridinium,1-(1-dodecyl)pyridinium,1-(1-tetradecyl)pyridinium, 1-(1-hexadecyl)pyridinium,1,2-dimethylpyridinium, 1-ethyl-2-methylpyridinium,1-(1-butyl)-2-methylpyridinium, 1-(1-hexyl)-2-methylpyridinium,1-(1-octyl)-2-methylpyridinium, 1-(1-dodecyl)-2-methylpyridinium,1-(1-tetradecyl)-2-methylpyridinium, 1-(1-hexadecyl)-2-methylpyridinium,1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium,1-(1-butyl)-2-ethylpyridinium, 1-(1-hexyl)-2-ethylpyridinium,1-(1-octyl)-2-ethylpyridinium, 1-(1-dodecyl)-2-ethylpyridinium,1-(1-tetradecyl)-2-ethylpyridinium, 1-(1-hexadecyl)-2-ethylpyridinium,1,2-dimethyl-5-ethylpyridinium, 1,5-diethyl-2-methylpyridinium,1-(1-butyl)-2-methyl-3-ethylpyridinium,1-(1-hexyl)-2-methyl-3-ethylpyridinium and1-(1-octyl)-2-methyl-3-ethylpyridinium,1-(1-dodecyl)-2-methyl-3-ethylpyridinium,1-(1-tetradecyl)-2-methyl-3-ethylpyridinium and1-(1-hexadecyl)-2-methyl-3-ethylpyridinium.

Especially preferred are ionic liquids IL in which the cation is apyridazinium cation of the formula (III) where

-   -   all the R⁴, R⁵, R⁶ and R⁷ radicals are hydrogen; or    -   one of the R⁴, R⁵, R⁶ and R⁷ radicals is methyl or ethyl and the        remaining R⁴, R⁵, R⁶ and R⁷ radicals are hydrogen.

Especially preferred are ionic liquids IL in which the cation is apyrimidinium cation of the formula (IIm) where

-   -   R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each        independently hydrogen or methyl; or    -   R⁴ is hydrogen, methyl or ethyl, R⁵ and R⁶ are methyl and R⁷ is        hydrogen.

Especially preferred are ionic liquids IL in which the cation is apyrazinium cation of the formula (IIn) where

-   -   R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each        independently hydrogen or methyl; or    -   R⁴ is hydrogen, methyl or ethyl, R⁵ and R⁶ are methyl and R⁷ is        hydrogen; or    -   R⁴, R⁵, R⁶ and R⁷ are methyl, or    -   R⁴, R⁵, R⁶ and R⁷ are hydrogen.

Especially preferred are ionic liquids IL in which the cation is animidazolium cation of the formula (IIo) where

-   -   R⁴ is hydrogen, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl,        1-hexyl, 1-octyl, 2-hydroxyethyl or 2-cyanoethyl and R⁵, R⁶ and        R⁷ are each independently hydrogen, methyl or ethyl.

Very particularly preferred imidazolium cations (IIo) include1-methylimidazolium, 1-ethylimidazolium, 1-(1-butyl)imidazolium,1-(1-octyl)imidazolium, 1-(1-dodecyl)imidazolium,1-(1-tetradecyl)imidazolium, 1-(1-hexadecyl)imidazolium,1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium,1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium,1-(1-hexyl)-3-methylimidazolium, 1-(1-hexyl)-3-ethylimidazolium,1-(1-hexyl)-3-butylimidazolium, 1-(1-octyl)-3-methylimidazolium,1-(1-octyl)-3-ethylimidazolium, 1-(1-octyl)-3-butylimidazolium,1-(1-dodecyl)-3-methylimidazolium, 1-(1-dodecyl)-3-ethylimidazolium,1-(1-dodecyl)-3-octylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium,1-(1-tetradecyl)-3-ethylimidazolium,1-(1-tetradecyl)-3-butylimidazolium,1-(1-tetradecyl)-3-octylimidazolium,1-(1-hexadecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-ethylimidazolium,1-(1-hexadecyl)-3-butylimidazolium, 1-(1-hexadecyl)-3-octylimidazolium,1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium,1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium,1-(1-hexyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium,1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium,3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium,1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium,1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazoliumand 1,4,5-trimethyl-3-octylimidazolium.

Especially preferred are ionic liquids IL in which the cation is apyrazolium cation of the formula (IIp) where

-   -   R⁴ is hydrogen, methyl or ethyl and R⁵, R⁶ and R⁷ are each        independently hydrogen or methyl.

Especially preferred are ionic liquids IL in which the cation is athiazolium cation of the formula (IIq) or (110 or an oxazolium cation ofthe formula (IIr) where

-   -   R⁴ is hydrogen, methyl, ethyl or phenyl and R⁵, R⁶ and R⁷ are        each independently hydrogen or methyl.

Especially preferred are ionic liquids IL in which the cation is a1,2,4-triazolium cation of the formula (IIs), (IIs′) or (IIs″) where

-   -   R⁴ and R⁵ are each independently hydrogen, methyl, ethyl or        phenyl and R⁶ is hydrogen, methyl or phenyl.

In a preferred embodiment, the ionic liquid IL, especially the at leastone ionic liquid IL2, comprises, as cation, at least one, preferablyexactly one, cation selected from the group consisting of pyridiniumcations, pyridazinium cations, pyrimidinium cations, pyrazinium cations,imidazolium cations, pyrazolium cations, thiazolium cations andtriazolium cations.

These cations are listed, for example, in WO 2005/113702. If necessaryfor a positive charge on the nitrogen atom or in the aromatic ringsystem, the nitrogen atoms are each substituted by an organic grouphaving generally not more than 20 carbon atoms, preferably a hydrocarbylgroup, especially a C₁-C₁₆ alkyl group, especially a C₁-C₁₀ alkyl groupand more preferably a C₁-C₄ alkyl group.

Particularly preferred cations of IL are imidazolium cations,pyrimidinium cations and pyrazolium cations, which are understood tomean compounds having an imidazolium, pyrimidinium or pyrazolium ringsystem and optionally any desired substituents on the carbon and/ornitrogen atoms of the ring system.

Particularly preferred cations of IL2 are imidazolium cations,pyridinium cations and pyrazolium cations, which are understood to meancompounds having an imidazolium, pyridinium or pyrazolium ring systemand optionally any desired substituents on the carbon and/or nitrogenatoms of the ring system.

Preferably, the ionic liquid IL, especially the at least one ionicliquid 1L2, comprises at least one, preferably exactly one, imidazoliumcation as cation. More preferably, the ionic liquid IL comprises, as thesole cation, at least one, preferably exactly one, imidazolium cation.

In a particularly preferred embodiment, the ionic liquid IL is acompound of the formula (III) comprising an imidazolium cation

in which

-   -   R, R⁴, R⁵, R⁶ and R⁷ are each as defined above;    -   X is an anion, and    -   n is 1, 2 or 3.

Preferably, the R⁴, R⁵, R⁶ and R⁷ and R⁸ radicals are each independentlyselected from hydrogen, C₁-C₁₂-alkyl, preferably C₁-C₆-alkyl, andhalogen, especially selected from hydrogen, methyl, ethyl, 1-propyl,1-butyl and chlorine.

The variable n is preferably 1.

Usable anions, especially as anion X^(n−), according to the formulae (I)and (III), are in principle any anions which, in conjunction with thecation, lead to an ionic liquid.

The anion, especially the anion X^(n−), may be an organic or inorganicanion. Particularly preferred ionic liquids consist exclusively of thesalt of an organic cation with one of the anions specified below.

The anion, especially the anion X^(n−) according to the formulae (I) and(III) of the ionic liquid IL, is, for example, selected from:

-   -   the group of the halides and halogen compounds of the formulae:    -   F⁻; Cl⁻; Br⁻; I⁻; BF₄ ⁻; PF₆ ⁻; AlCl₄ ⁻; Al₂Cl₇ ⁻, Al₃Cl₁₀ ⁻,        AlBr₄ ⁻; CF₃SO₃ ⁻; (CF₃SO₃)₂N⁻, CF₃CO₂ ⁻, CCl₃CO₂ ⁻; CN⁻, SCN⁻,        OCN⁻, NO₂ ⁻, NO₃ ⁻;    -   the group of the sulfates, sulfites and sulfonates of the        formulae:    -   SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, HSO₃ ⁻, R^(a)OSO₃ ⁻, R^(a)SO₃ ⁻;    -   the group of the phosphates of the formulae:    -   PO₄ ³⁻, H PO₄ ²⁻, H₂PO₄ ⁻, R^(a)PO₄ ²⁻, HR^(a)PO₄—,        R^(a)R^(b)PO₄ ⁻;    -   the group of the phosphonates and phosphinates of the formulae:    -   R^(a)HPO₃ ⁻, R^(a)R^(b)PO₂ ⁻, R^(a)R^(b)PO₃ ⁻;    -   the group of the carboxylates of the general formula:    -   R^(a)COO⁻;    -   the group of the borates of the general formulae:    -   BO₃ ³⁻, HBO₃ ²⁻, H₂BO₃ ⁻, R^(a)R^(b)BO₃ ⁻, R^(a)HBO₃ ⁻, R^(a)BO₃        ²⁻, B(OR^(a))(OR^(b))(OR^(c))(OR^(d))⁻, B(HSO₄)⁻, B(R^(a)SO₄)⁻;    -   the group of the boronates of the general formulae:    -   R^(a)BO₂ ²⁻, R^(a)R^(b)BO⁻;    -   the group of the carbonates and carbonic esters of the general        formulae:    -   HCO₃ ⁻, CO₃ ²⁻, R^(a)CO₃ ⁻;    -   the group of the carboximides, bis(sulfonyl)imides and        sulfonylimides of the general formulae:

-   -   the group of the alkoxides and aryl oxides of the general        formula:    -   R^(a)O⁻;

where R^(a), R^(b), R^(c) and R^(d) in the aforementioned anions areeach independently selected from:

-   -   hydrogen or C₁-C₁₂-alkyl and the cycloalkyl-, halogen-,        hydroxyl-, amino-, carboxyl-, formyl-, —O—, —CO—, —CO—O— or        —CO—N<-substituted components thereof, for example methyl,        ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl        (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl,        3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl,        3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl,        3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,        4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,        4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,        2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,        3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,        3,3-dimethyl-2-butyl, heptyl, octyl, nonyl, decyl, undecyl,        dodecyl, methoxy, ethoxy, formyl, acetyl or CF₃.

More preferably, R^(a), R^(b), R^(c) and R^(d) in the aforementionedanions are each independently a hydrogen atom or an unsubstitutedC₁-C₁₂-alkyl group, preferably C₁-C₆-alkyl group.

Particularly preferred anions, especially very particularly preferredanions X^(n−), are:

chloride, bromide, hydrogensulfate, tetrachloroaluminate, thiocyanate,methylcarbonate, methylsulfate, ethylsulfate, methanesulfonate, formate,acetate, dimethylphosphate, diethylphosphate, p-tolylsulfonate,tetrafluoroborate, hexafluorophosphate,bis(trifluoromethylsulfonyl)imide and bis(methylsulfonyl)imide.

Very particularly preferred anions, especially very particularlypreferred anions X^(n−), are:

chloride, hydrogensulfate, methylsulfate, ethylsulfate,methanesulfonate, formate and acetate.

Especially preferred are ionic liquids IL comprising, as cation, atleast one cation, preferably exactly one cation, selected from the groupconsisting of

-   -   1-methylimidazolium, 1-ethylimidazolium, 1-(1-butyl)imidazolium,        1-(1-octyl)imidazolium, 1-(1-dodecyl)imidazolium,        1-(1-tetradecyl)imidazolium, 1-(1-hexadecyl)imidazolium,        1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium,        1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium,        1-(1-hexyl)-3-methylimidazolium, 1-(1-hexyl)-3-ethylimidazolium,        1-(1-hexyl)-3-butylimidazolium, 1-(1-octyl)-3-methylimidazolium,        1-(1-octyl)-3-ethylimidazolium, 1-(1-octyl)-3-butylimidazolium,        1-(1-dodecyl)-3-methylimidazolium,        1-(1-dodecyl)-3-ethylimidazolium,        1-(1-dodecyl)-3-butylimidazolium,        1-(1-dodecyl)-3-octylimidazolium,        1-(1-tetradecyl-3-methylimidazolium,        1-(1-tetradecyl)-3-ethylimidazolium,        1-(1-tetradecyl)-3-butylimidazolium,        1-(1-tetradecyl-3-octylimidazolium,        1-(1-hexadecyl)-3-methylimidazolium,        1-(1-hexadecyl)-3-ethylimidazolium,        1-(1-hexadecyl)-3-butylimidazolium,        1-(1-hexadecyl-3-octylimidazolium, 1,2-dimethylimidazolium,        1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium,        1-(1-butyl)-2,3-dimethylimidazolium,        1-(1-hexyl)-2,3-dimethylimidazolium,        1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium,        1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium,        3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium,        1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium,        1,4,5-trimethyl-3-ethylimidazolium,        1,4,5-trimethyl-3-butylimidazolium,        1,4,5-trimethyl-3-octylimidazolium; and        1-butyl-1-methylpyrrolidinium;

and, as anion, at least one anion, preferably exactly one anion,selected from the group consisting of

-   -   chloride, bromide, hydrogensulfate, tetrachloroaluminate,        thiocyanate, methylsulfate, ethylsulfate, methanesulfonate,        formate, acetate, dimethylphosphate, diethylphosphate,        p-tolylsulfonate, tetrafluoroborate and hexafluorophosphate.

Particular preference is additionally given to ionic liquids IL selectedfrom the group consisting of:

-   -   1,3-dimethylimidazolium methylsulfate, 1,3-dimethylimidazolium        hydrogensulfate, 1,3-dimethylimidazolium dimethylphosphate,        1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium        methylsulfate, 1-ethyl-3-methylimidazolium ethylsulfate,        1-ethyl-3-methylimidazolium hydrogensulfate,        1-ethyl-3-methylimidazolium thiocyanate,        1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium        methanesulfonate, 1-ethyl-3-methylimidazolium diethylphosphate,        1-(1-butyl)-3-methylimidazolium methylsulfate,        1-(1-butyl)-3-methylimidazolium hydrogensulfate,        1-(1-butyl)-3-methylimidazolium thiocyanate,        1-(1-butyl)-3-methylimidazolium acetate,        1-(1-butyl)-3-methylimidazolium methanesulfonate,        methyltri(1-butyl)ammonium methylsulfate,        1-butyl-1-methylpyrrolidinium dimethylphosphate,        N,N-dimethylpiperidinium and N,N-dimethylmorpholinium.

In a particularly preferred embodiment, the composition C comprises atleast one ionic liquid IL selected from the group consisting of1-ethyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazoliumethylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazoliummethanesulfonate, methyltri(1-butyl)ammonium methylsulfate (MTBS) and1-butyl-1-methylpyrrolidinium dimethylphosphate.

In one embodiment, the composition C comprises

-   -   as the first ionic liquid IL1 methyltri(1-butyl)ammonium        methylsulfate (MTBS);    -   and as the second ionic liquid 1L2 a compound selected from the        group consisting of    -   1,3-dimethylimidazolium methylsulfate, 1,3-dimethylimidazolium        hydrogensulfate, 1,3-dimethylimidazolium dimethylphosphate,        1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium        methylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,        1-ethyl-3-methylimidazolium thiocyanate,        1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium        methanesulfonate, 1-ethyl-3-methylimidazolium diethylphosphate,        1-(1-butyl)-3-methylimidazolium methylsulfate,        1-(1-butyl)-3-methylimidazolium hydrogensulfate,        1-(1-butyl)-3-methylimidazolium thiocyanate,        1-(1-butyl)-3-methylimidazolium acetate,        1-(1-butyl)-3-methylimidazolium methanesulfonate,        1-(1-dodecyl)-3-methylimidazolium methylsulfate,        1-(1-dodecyl)-3-methylimidazolium hydrogensulfate,        1-(1-tetradecyl)-3-methylimidazolium methylsulfate,        1-(1-tetradecyl)-3-methylimidazolium hydrogensulfate,        1-(1-hexadecyl)-3-methylimidazolium methylsulfate and        1-(1-hexadecyl)-3-methylimidazolium hydrogensulfate,    -   preferably selected from 1-ethyl-3-methylimidazolium        methylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,        1-ethyl-3-methylimidazolium acetate and        1-ethyl-3-methylimidazolium methanesulfonate.

Further constituents of composition C

The composition of the invention and the composition C used in theprocess of the invention may comprise further constituents in additionto the at least one ionic liquid IL.

Possible examples of these include additives with which a desiredviscosity and/or a desired melting point is established. These include,for example, solvents, especially water and/or organic solvents misciblewith the ionic liquid.

In a preferred embodiment, the composition C comprises:

-   -   0% to 100% by weight, preferably 60% to 90% by weight and more        preferably 60% to 80% by weight, based on the overall        composition C, of the at least one ionic liquid IL;    -   0% to 45% by weight, preferably 0% to 30% by weight, more        preferably 1% to 30% by weight and most preferably 5% to 20% by        weight, based on the overall composition C, of at least one        solvent S.

In a preferred embodiment, the composition C consists of theabovementioned components, i.e. the abovementioned components add up to100% by weight.

Preferably, the composition C is a solution; more particularly, thecomponents of composition C are homogeneously miscible with one anotheror the components of composition C are in homogeneously distributedform. More particularly, the composition C is a solution havingmolecular dispersion.

The composition C may especially comprise water or an organic solventmiscible with water and the ionic liquid IL or a mixture thereof assolvent S.

The viscosity of the composition C (etch composition) is preferably inthe range from 20 to 200 mPas, preferably in the range from 30 to 100mPas and more preferably in the range from 30 to 70 mPas (in each caseby dynamic means at 60° C.).

The melting point of the composition C is typically below 100° C.,preferably below room temperature (25° C.), especially preferably below10° C., more preferably below 0° C.

Preferably, the composition C comprises at least one solvent S selectedfrom water, propylene carbonate, polyethylene glycols, mono-, di- ortriesters of glycol and C₁-C₆ carboxylic acids, especially diacetin(glyceryl diacetate) and triacetin (glyceryl triacetate), glycols,especially ethylene glycol, diethylene glycol, triethylene glycol andtetraethylene glycol. Preference is given to polyethylene glycols havinga molecular weight in the range of 200-4000 g/mol, preferably 200-1000g/mol, more preferably 200-600 g/mol.

More preferably, the composition C comprises 1% to 30% by weight,preferably 5% to 20% by weight and more preferably 7% to 15% by weight,based on the overall composition C, of at least one solvent S selectedfrom propylene carbonate, polyethylene glycol, especially PEG 200,triacetin and water.

In a preferred embodiment, the composition C comprises:

-   -   49% to 94% by weight, preferably 55% to 85% by weight and more        preferably 60% to 80% by weight, based on the overall        composition C, of at least one above-described ionic liquid IL        comprising at least one alkylammonium cation;    -   5% to 50% by weight, preferably 5 to 40% by weight, preferably        10% to 40% by weight, also preferably 5 to 20% by weight and        more preferably 10% to 20% by weight, based on the overall        composition C, of at least one above-described ionic liquid IL2        comprising, as cation, at least one aromatic heterocycle having        a delocalized cationic charge and comprising at least one        nitrogen atom;    -   1% to 30% by weight, preferably 5% to 20% by weight, based on        the overall composition C, of at least one solvent S selected        from the group consisting of water, propylene carbonate,        polyethylene glycols, mono-, di- or triesters of glycol and        C₁-C₆ carboxylic acids, and glycols, preferably selected from        the group consisting of water, propylene carbonate, polyethylene        glycols, diacetin (glyceryl diacetate), triacetin (glyceryl        triacetate), ethylene glycol, diethylene glycol, triethylene        glycol and tetraethylene glycol.

In another preferred embodiment, the composition C comprises

-   -   49% to 94% by weight, preferably 55% to 85% by weight and more        preferably 60% to 80% by weight, based on the overall        composition C, of the at least one ionic liquid IL1;    -   5% to 50% by weight, preferably 5% to 30% by weight and more        preferably 5% to 20% by weight, based on the overall composition        C, of the at least one ionic liquid IL2;    -   1% to 30% by weight, preferably 10% to 30% by weight, based on        the overall composition C, of at least one solvent S as        described above.

In a preferred embodiment, the composition C comprises exclusivelypropylene carbonate as solvent S. It is additionally possible that thecomposition comprises a mixture of propylene carbonate and water assolvent S, in which case the proportion of propylene carbonate, based onthe overall solvent S, is at least 30% by weight, preferably at least50% by weight, more preferably at least 90% by weight.

The composition consists preferably to an extent of more than 10% byweight, especially to an extent of more than 30% by weight, morepreferably to an extent of more than 50% by weight and most preferablyto an extent of more than 80% by weight of the at least one ionic liquidIL. In a particularly preferred embodiment, it consists to an extent ofmore than 90% by weight and especially to an extent of more than 95% byweight of the at least one ionic liquid IL. In a further embodiment, thecomposition consists exclusively of one or more of the above-describedionic liquids, preferably of the ionic liquids IL1 and IL2.

The ionic liquid and composition C which comprises or consists of theionic liquid are preferably liquid over the entire temperature rangefrom 20 to 100° C. (at standard pressure, 1 bar).

The process

An essential element in the process of the invention is the pretreatmentaccording to the claims of the plastics or the plastic surface. Thevarious process steps for chemical and electrolytic coating with metaland further measures for performance, preparation and finishing that arenecessary or advisable for the purpose are described in a wide varietyof different embodiments in the prior art, for example in DE-A 100 54544, Schlesinger et al. “Modern Electroplating” chapter 18, pages450-457 (5th edition, 2010, John Wiley & Sons Inc., ISBN978-0-470-16778-6) or Kanani “Galvanotechnik” [ElectroplatingTechnology] (Carl Hanser Verlag, 2000, ISBN 3-446-21024-5).

Even prior to the pretreatment of the invention in step a), cleaningand/or degreasing of the plastic surface to be coated may be advisable.Cleaning and degreasing of this kind can be conducted with standardcleaning compositions or detergents.

Step a)

The process of the invention comprises, in step a), the pretreatment ofthe plastic surface with a composition C (etch solution) comprising atleast one ionic liquid IL. Preferred ionic liquids and optional furtherconstituents of the composition C are described above.

It has been found that, surprisingly, observing optimized treatmentconditions, especially the temperature and duration of the pretreatment,gives particularly advantageous metal coatings.

Preferably, the pretreatment of the plastic surface with the compositionC in step a) is effected at a temperature of 30 to 120° C., morepreferably of 40 to 120° C., especially preferably of 50 to 65° C. andmost preferably 50 to 60° C. Preferably, the composition C has the abovetemperature for the purpose. There is often no need for precedingseparate heating of the plastic surface to be coated, or of the plasticmolding to be coated.

Preferably, the pretreatment of the plastic surface with the compositionC in step a) is effected over a period of 1 to 60 min, preferably 1 to30 min, especially preferably 2 to 20 min and more preferably 5 to 10min.

Preferably, the pretreatment of the plastic surface with the compositionC in step a) is effected at a temperature in the range from 50 to 65° C.and over a period of 5 to 20 min. More preferably, the pretreatment ofthe plastic surface with the composition C in step a) is effected at atemperature in the range from 50 to 60° C. and over a period of 5 to 15min.

In a preferred embodiment, the invention relates to a process forcoating a plastic surface, especially a plastic molding, consisting ofor comprising acrylonitrile/butadiene/styrene copolymer ABS, wherein thepretreatment of the plastic surface, especially of the plastic molding,with the composition C in step a) is effected at a temperature in therange from 50 to 60° C., preferably 50 to 55° C., and over a period of 5to 15 min, preferably 5 to 10 min. The plastic surface consisting orcomprising acrylonitrile/butadiene/styrene copolymer (ABS) mayespecially be a plastic molding consisting essentially of ABS, of ablend comprising ABS, e.g. ABS/PC (acrylonitrile/butadiene/styrenecopolymer and polycarbonate), and/or a multicomponent plastic comprisingABS.

In a preferred embodiment, the plastic surface to be coated, especiallythe plastic molding to be coated, is dipped into the composition C,where the composition C preferably has the above temperature. In thiscase, the composition C can be agitated for better mass transfer, whichcan be effected by stirring, pumping, blowing air in, etc.Alternatively, the plastic surface itself can also be agitated in thecomposition C by means of specific devices known in electroplating. Theperson skilled in the art is aware of suitable methods for the purpose.

The required amount of composition C is adjusted in such a way that theplastic surface is wetted to the desired degree. The plastic surface orthe plastic molding can be immersed completely or else partially.

The viscosity of the composition C (etch solution) is preferably in therange from 20 to 200 mPas, preferably in the range from 30 to 100 mPasand more preferably in the range from 30 to 70 mPas (dyn., 60° C.).

Step b)

The process of the invention comprises, in step b), the treating of theplastic surface from step a) with an aqueous rinse solution RS whileapplying ultrasound. The treatment in step b) can especially remove theadhering composition C, but also partly dissolved plastic particles,from the surface, especially from the surface of the plastic molding.

In a preferred embodiment, the treating of the plastic surface with theaqueous rinse solution RS with application of ultrasound in step b) iseffected by dipping the plastic surface from step a) into an ultrasoundbath comprising the aqueous rinse solution RS for a period of 1 to 30min, preferably 2 to 20 min and more preferably 5 to 15 min. Inparticular an sufficient rinsing might be obtained after 1 to 2 min, inparticular at about 90 sec. Preferably, step b) is effected by dippingthe plastic surface from step a) into an ultrasound bath comprising theaqueous rinse solution RS for a period of 1 to 2 min at a temperature inthe range from 40 to 60° C.

In a preferred embodiment, the treating of the plastic surface,especially the plastic molding, with the aqueous rinse solution RS whileapplying ultrasound in step b) is effected by dipping the plasticsurface, especially the plastic molding, from a) into an ultrasound bathcomprising the aqueous rinse solution RS at a power in the range from 40to 60 watts/L, over a period of 1 to 30 min and at a temperature of 40to 60°, and wherein the aqueous rinse solution RS comprises at least 85%by weight of water, preferably at least 95% by weight.

The aqueous rinse solution RS preferably comprises water or a mixture ofwater and one or more water-miscible organic solvents, where theproportion of water is generally at least 85% by weight, preferably atleast 95% by weight and more preferably at least 98% by weight, based ineach case on the overall rinse solution. Organic solvents used may beknown polar water-miscible solvents such as alcohols or dimethylsulfoxide (DMSO). Organic solvents used may especially be water-misciblealcohols such as methanol, ethanol or propanol. In a preferredembodiment, the rinse solution RS consists exclusively of water.

The rinse solution RS may optionally comprise the additions known tothose skilled in the art, for example surfactants.

The pH of the rinse solution RS is preferably in the range from 5 to 8,especially from 6 to 7. Preferably, the rinse step b), which may alsoconsist of a plurality of steps, is conducted at a temperature in therange from 10 to 80° C., preferably 20 to 70° C., more preferably at 40to 60° C.

The ultrasound treatment is preferably effected at frequencies in therange from 20 to 400 kHz, preferably 30 to 50 kHz. The ultrasoundtreatment is preferably effected at a power in the range from 10 to 100watts/L, preferably from 40 to 60 watts/L. Especially preferably, theultrasound treatment is effected at a power in the range from 40 to 60watts/L, over a period of 5 to 15 min and a temperature of 40 to 60° C.Further preferred, the ultrasound treatment is effected at a power inthe range from 40 to 60 watts/L, over a period of 1 to 2 min and atemperature of 40 to 60° C.

Preferably, step b) may comprise a plurality of rinse steps, especiallyfurther rinse steps without application of ultrasound. Preferably, thetreating of the plastic surface with an aqueous rinse solution RS instep b) may comprise, as an additional step, the treating of the plasticsurface with at least one further aqueous rinse solution RS, especiallywater, which may be effected, for example, by spraying or dipping theplastic surface.

A preferred embodiment relates to a process as described, wherein stepb) comprises (and preferably consists of) the following steps:

-   -   b1) treating the plastic surface, especially the plastic        molding, from step a) with a first aqueous rinse solution RS1,        by spraying the plastic surface, especially the plastic molding,        with the first aqueous rinse solution RS1 or dipping it into the        first aqueous rinse solution RS1;    -   b2) treating the plastic surface, especially the plastic        molding, from step b1) with a second aqueous rinse solution RS2        while applying ultrasound.

The process of the invention, especially steps a) and/or b), can beconducted partly or fully continuously or quasi-continuously.

In one embodiment, the composition C is recovered after step a) and fedfully or partly back to the etching step a) (recycling). The recyclingof the composition C can be effected, for example, by a precipitation ofthe dissolved plastic by means of water or an organic solvent andsubsequent removal of the dissolved plastic by a filtration. Themedium/media utilized for precipitation can subsequently be recovered bydistillation. It is also possible to remove volatile constituents of thedissolved plastic from the composition by direct distillation. In thisway, it is possible to obtain a purified and reusable composition C.

In a preferred embodiment, the rinse solution RS is recovered after stepb), especially after steps b1) and/or b2), and fed fully or partly backto the rinse steps b), especially the rinse steps b1) and/or b2)(recycling). Preferably, the spent rinse solution is cleaned beforehand,for example by filtration.

The recycling of the rinse solutions RS can be effected, for example, byremoving the plastic present therein, preferably by a filtration. Inthis way, it is possible to obtain a cleaned and reusable rinse solution(which is generally a mixture of water and ionic liquid IL) which canthen be recycled fully or partly to rinse steps b1) and/or b2).Preferably, a portion of the rinse solution recovered is discharged,especially in order to prevent enrichment of ionic liquid in the rinsesolution RS in the circuit.

Step c)

The process of the invention comprises, in step c), the treating of theplastic surface from step b) with an activator composition A comprisingat least one ionogenic and/or colloidal activator, especially at leastone palladium component P, preferably at least one colloidal palladiumcomponent P.

Typically, step c) comprises, especially in combination with step d),the applying of metal nuclei, preferably of metal nuclei of palladium,silver or gold, more preferably of palladium. Step b) is typicallyreferred to as activation. Preferably, the manner of activation and thefirst metal coating in step e) are matched to one another.

Known methods for activation are, for example, conventional colloidalactivation (application of palladium/tin colloids), ionogenic activation(application of palladium cations), direct metallization or processesknown by the Udique Plato®, Enplate MID select or LDS Process names.

For example, activation with ionogenic systems can be accomplished byfirst treating the plastic surface with tin(II) ions, generally withformation of firmly adhering gels of tin oxide hydrate on rinsing withwater after the treatment with the tin(II) ions. In the subsequenttreatment with a palladium salt solution, palladium nuclei are normallyformed on the plastic surface through reduction with the tin(II)species, and these typically serve as catalyst/metal nucleus for thelater chemical metallization (step e)).

For activation with colloidal systems, it is possible to use noble metalcolloid compositions, especially colloids of the gold group (transitiongroup I) and platinum group of the Periodic Table. Preference is givento using colloidal solutions of palladium, silver or gold, especiallypreferably colloidal solutions of palladium. In the colloidal solution,the metal nuclei, for example the palladium nuclei, are typicallysurrounded by the protective colloid shell. It is possible withpreference to use palladium colloid solutions which form throughreaction of palladium chloride with tin(II) chloride in the presence ofexcess hydrochloric acid.

The concentration of the at least one ionogenic and/or colloidalactivator P in the activator composition A is typically 20 to 150 mg/L.

Typical palladium-containing activator systems and further details ofthe activation step are described in Annual Book of ASTM Standard, Vol.02.05 “Metallic and Inorganic Coatings; Metal Powders, Sintered P/MStructural Parts”, Standard Practice for Preparation of PlasticMaterials for Electroplating, 1995, pages 446-450.

Typically, the activator P used may be a standard commercially availablepalladium activator, for example “Activator U” from HSO or “Surtec 961Pd” from Surtec.

Step d)

The process of the invention comprises, in step d), the treating of theplastic surface from step c) with an accelerator composition Bcomprising an acid and/or a reducing agent.

The treatment of the plastic surface with the accelerator composition Bespecially frees the metal nuclei adsorbed on the surface (especially inthe depressions), especially palladium, silver or gold nuclei, of theprotective colloid shell and/or reduces the absorbed metal salts to themetal. The treatment of the plastic surface with the acceleratorcomposition B typically gives rise to metal nuclei on the plasticsurface, preferably metal nuclei of palladium, silver or gold, morepreferably of palladium. These metal nuclei typically serve as thestarting point (catalyst) for the subsequent chemical metal depositionin step e).

According to the invention, the accelerator composition B comprises atleast one reducing agent and/or an acid which is particularly suitablefor removing the protective metal colloid shell and/or for reducingmetal salts present at the surface to the metal. Preferably, the atleast one reducing agent is selected from alkali metal, ammonium oralkaline earth metal fluoroborate, for example sodium tetrafluoroborate(NaBF₄), peroxides, sulfites, hydrogensulfites, hydrazine and saltsthereof, hydroxylamine and salts thereof. Preferably, the at least oneacid is selected from hydrochloric acid, methanesulfonic acid, citricacid, ascorbic acid, tartaric acid, tetrafluoroboric acid (HBF₄).

The pH of the accelerator composition B may especially be set within arange from 0 to 7, preferably from 1 to 2.

The concentration of the acid and/or the reducing agent in theaccelerator composition B is typically 0.4 to 0.5 N; the concentrationis especially 0.45 N (pH 1.5).

Typical accelerator compositions and further details of the accelerationstep are described in Annual Book of ASTM Standard, Vol. 02.05 “Metallicand Inorganic Coatings; Metal Powders, Sintered P/M Structural Parts”,Standard Practice for Preparation of Plastic Materials forElectroplating, 1995, pages 446-450.

Typically, the accelerator composition B used may be a standardcommercially available accelerator, for example “HSO Accelerator” fromHSO or “Surtec 961 A” from Surtec.

Step e)

A further constituent of the process of the invention is the applicationof what is called a first metal coating, which is typically effected byelectroless means (chemical metal deposition). In general, the firstlayer applied by electroless means (seed layer) is a layer of nickel,copper, chromium or alloys thereof. Preference is given to one or morelayers of nickel and/or copper. Particular preference is given toexactly one layer consisting essentially of nickel.

The process of the invention comprises, in step e), the chemicaldeposition of a metal layer, preferably of a metal layer consistingessentially of nickel, by treating the plastic surface, especially theplastic molding, from step d) with a coating composition M1 comprisingat least one metal salt, preferably at least one nickel(II) salt, and atleast one reducing agent, preferably an in situ reducing agent.

Further preferably, step e) comprises the chemical deposition of a metallayer consisting essentially of nickel and/or copper, by treating thesurface from step d) with a coating composition M1 comprising at leastone nickel(II) salt and/or one copper(II) salt, and at least onereducing agent, preferably an in situ reducing agent.

Typical coating compositions M1 are described, for example, inSchlesinger et al. “Modern Electroplating” (5th edition, 2010, JohnWiley & Sons Inc., ISBN 978-0-470-16778-6) on page 451.

Preferably, the plastic surface or the plastic molding from step d) iscoated with a metal layer consisting of nickel, copper, chromium oralloys thereof, more preferably of nickel or a nickel alloy.

Preferably, the metal salt is selected from nickel, copper and chromiumsalts, for example halides or sulfates. Preferably, the coatingcomposition M1 comprises at least one nickel salt, for example nickelsulfate.

The concentration of the at least one metal salt, especially of the atleast one nickel salt, in the coating composition M1 is typically in therange from 15 to 35 g/L.

The pH of the coating composition M1 is typically in the range from 4 to11. In principle, according to the type of buffer system, a distinctionmay be made between acidic or alkaline compositions. In the case of theacidic methods, the pH of the coating composition M1 is typically in therange from 4 to 7, preferably 4 to 6. In the case of alkaline methods,the pH is typically in the range from greater than 7 to 11, preferably 8to 10. Preferably, the pH is set to about 9.

Preferably, the coating composition M1 comprises at least one reducingagent, especially an in situ reducing agent, selected from the groupconsisting of hydrogen peroxide, peroxides, hypophosphites,hypophosphates (e.g. sodium hypophosphate), borane and boranederivatives (e.g. aminoborane such as dimethylaminoborane, sodiumborohydride) and hydrazine.

The concentration of reducing agent in the coating composition M1 istypically 15 to 30 g/L.

Typically, the coating composition M1 for chemical nickel baths maycomprise typical further components and additives known to those skilledin the art, as described, for example, in chapter 18.3 in Schlesinger etal. “Modern Electroplating” (5th edition, 2010, John Wiley & Sons Inc.,ISBN 978-0-470-16778-6). Typically, the coating composition M1 maycomprise complexing agents for the nickel ions, preferably carboxylicacids and hydroxycarboxylic acids, for example succinic acid, citricacid, malic acid, tartaric acid and/or lactic acid, and acetic acid,propionic acid, maleic acid, fumaric acid and/or itaconic acid. Buffersused may typically be citrates, acetates, phosphates and ammonium salts.

Typically, the coating composition M1 used may be a standardcommercially available coating bath for electroless nickel deposition,for example “Electroless Nickel 601KB” from HSO or “Surtec 3/11D” fromSurtec.

The temperature of the coating composition M1 during the performance ofstep d) in the case of acidic processes is typically 60 to 100° C. andin the case of alkaline processes typically in the range from 25 to 50°C.

Step f)

Step f) of the process of the invention, finally, comprises theelectrochemical deposition of metal layers, preferably of one or morelayers consisting essentially of nickel, copper and/or chromium. Step f)may especially comprise one, two or more than two differentelectrochemical coatings.

By the process of the invention, it is possible to improve the adhesionof the metal layers, especially of the chemically deposited nickel layerdescribed and of the subsequent electrochemically deposited nickel,copper and chromium layer, to plastic surfaces, for example made fromABS, or to actually make said adhesion possible at all for manyplastics. The achieved adhesion of the metal layers is very good, evenin the event of mechanical stress or high temperatures. In addition, themetal surfaces obtained by the process of the invention have aparticularly advantageous regular structure.

The process of the invention comprises, in step f), the electrochemicalcoating of the plastic surface, especially the plastic molding, fromstep e) with at least one further metallic layer, by electrochemicallytreating the plastic surface, especially the plastic molding, from stepe) with at least one coating composition M′ comprising at least onemetal compound.

Preferably, step f) comprises the electrochemical coating of the plasticsurface, especially the plastic molding, with at least one metalliclayer consisting essentially of copper. For this purpose, the plasticsurface, especially the plastic molding, is subjected to anelectrochemical electrolysis with a coating composition M2 comprising atleast one copper compound, preferably at least one copper(II) salt.

Preferably, step f) comprises the electrochemical coating of the plasticsurface, especially the plastic molding, with at least one metalliclayer consisting essentially of chromium. For this purpose, the plasticsurface, especially the plastic molding, is preferably contacted with acoating composition M3 comprising at least one chromium compound,preferably selected from chromic acid, chromic acid derivatives,chromium(VI) salts and chromium(III) salts, and subjected to anelectrochemical electrolysis.

Preferably, the invention relates to a process as described above,wherein the electrochemical coating in step f) comprises (and preferablyconsists of) the following steps:

-   -   f1) electrochemically coating the surface, especially the        plastic molding, from step e) with a layer consisting        essentially of copper and/or nickel, by treating the surface,        especially the plastic molding, from step e) with a coating        composition M2 comprising at least one copper compound,        especially a Cu(II) salt, and/or at least one nickel compound,        especially an Ni(II) salt; and    -   f2) electrochemically coating the surface, especially the        plastic molding, from step f1) with a layer consisting        essentially of chromium, by treating the surface, especially the        plastic molding, from step f1) with a coating composition M3        comprising at least one chromium compound, especially comprising        at least one chromium compound selected from chromic acid,        chromic acid derivatives, chromium(VI) salts and chromium(III)        salts.

Preferably, in step f1), the surface from step e) is electrochemicallycoated with a layer consisting essentially of copper, by treating thesurface from step e) with a coating composition M2 comprising at leastone copper compound, especially comprising at least one Cu(II) salt.

Further preferably, in step f1), the surface from step e) iselectrochemically coated with one or more layers consisting essentiallyof copper and one or more layers consisting essentially of chromium.Preferred coating sequences (steps e), f1) and f2)) may be as follows:

Ni (chem)→SB—Ni→B—Ni→Cr or Ni (chem)→Cu→SB—Ni→B—Ni→Cr or Cu(chem)→SB—Ni→B—Ni→Cr or Cu (chem)→Cu→SB—Ni→B—Ni→Cr;

where SB-Ni is a semibright nickel layer and B-Ni is a bright nickellayer.

Typically, the coating composition M2 comprises at least one coppersalt, preferably at least one copper(II) salt, for example coppersulfate (CuSO₄). Typically, the coating composition M2 comprises atleast one copper salt, water and an acid, for example sulfuric acid,alkylsulfonic acids such as methane sulfonic acid. Typically, thecoating composition M2 may comprise as a further additive an additivecustomary for this application, for example a surfactant, a brightener,suppressors or levelers.

Typically, the coating composition M2 used may be a standardcommercially available copper electrolysis bath, for example “Copper HD500” from HSO or “Surtec 867” from Surtec.

Typically, the coating composition M3 comprises at least one chromiumsalt and/or chromic acid, preferably at least one chromium(III) saltand/or one chromium(VI) salt, more preferably chromic acid H₂CrO₄ and/orchromium trioxide CrO₃. Typically, the coating composition M3 comprisesat least one chromium compound, especially chromic acid, water and anacid as catalyst, for example at least one acid selected from sulfuricacid (H₂SO₄), hydrofluoric acid (HF), hexafluorosilicic acid (H₂SiF₆),alkylsulfonic acids such as methane sulfonic acid. Typically, thecoating composition M3 may comprise, as further additive, a surfactantknown for this application.

The process of the invention may comprise one or more rinse steps, ineach case before and/or after the steps a) to f) described. Especiallyafter step f), the plastic surfaces, especially the plastic moldings,may be rinsed, preferably rinsed with water, and/or dried.

DESCRIPTION OF THE FIGURE

The electron micrographs in FIG. 1 show ABS surfaces which have beenobtained according to comparative example C1 (with a simple rinse step)(upper image) and ABS surfaces which have been obtained according toinventive example I1 with ultrasound treatment according to theinvention (lower image). In examples C1 and I1, an etchant composed ofMTBS:EMIM-OAc (95:5) was used. The ABS surfaces were etched at 70° C.for 10 min.

FIG. 2 shows one possible configuration of steps a) and b) of theinvention. The labels here have the following meanings:

-   -   (I) pretreatment bath (step a)    -   (II) collecting vessel of the spray apparatus (step b1)    -   (III) spray nozzles (step b1)    -   (IV) ultrasound rinse bath (step b2)    -   (V), (VI) filters    -   (1) onward route of the molding to (II)    -   (2) onward route of the molding to (IV)    -   (3) removal of the spray solution, first spray solution    -   (4) removal of the ultrasound bath rinse solution, second rinse        solution    -   (5) onward route of the cleaned rinse solutions    -   (5.1), (5.2) recycling of the cleaned rinse solution to        (II)/(IV)    -   (6.1), (6.2) discharge of the plastic removed    -   (7) discharge of a portion of the cleaned rinse solution

FIG. 2 shows one embodiment of process steps a), b1) and b2). Themolding is immersed into the treatment bath (I) comprising at least oneionic liquid IL (step a). When the molding is moved onward via (1) tothe spray step (spray apparatus consisting of (II) and (III)), a portionof the ionic liquid and partly dissolved plastic particles on thesurface of the molding are entrained therewith. In the spray apparatus(collecting vessel (II) and spray nozzles (III)), adhering composition Cis rinsed off the molding by spraying the molding with the first rinsesolution RS (step b1). The spent rinse solution is collected in thecollecting vessel and conducted via (3) to the filter (VI). When themolding is moved onward via (2) to the ultrasound rinse bath (IV)comprising the second rinse solution RS (step b2)), a portion of theionic liquid and of the first rinse solution and partly dissolvedplastic particles on the surface of the molding are again entrainedtherewith. The molding is immersed into the ultrasound bath, removedfrom the bath after the dwell time and sent to the further processsteps. In the ultrasound bath (IV), in a continuous manner, the secondrinse solution is removed from the bath via (4) and fed to the filter(V). In addition, there is a feed of cleaned rinse solution via (5),(5.1) and (5.2) to (II) and (IV). In the filters (V) and (VI), thepolymer is filtered out of the spent rinse solutions and discharged. Thecleaned rinse solutions are recycled via (5) to the process; a portionis discharged via (7).

The invention is illustrated in detail by the examples which follow.

EXAMPLE 1

1.1 General Test Method for Examination of Etching Action

A plaque of dimensions 60×30×2 mm of ABS(acrylonitrile/butadiene/styrene terpolymer Terluran® GP 35 fromStyrolution) is immersed at 70° C. into 2 L of stirred ionic liquid(composition C) for 10 minutes. After the etching has ended, thesubstrate is rinsed with water. In the inventive example, the plaque issubsequently treated in an ultrasound water bath.

The etching action is checked by means of SEM analysis and shows newstructuring of the surface (see FIG. 1).

1.2 Comparison of the Etching Outcome With and Without an UltrasoundRinse Step

The etching steps were conducted as described above on ABS test plaques,using an etch solution composed of methyltri(1-butyl)ammoniummethylsulfate (MTBS) and 1-ethyl-3-methylimidazolium acetate (EMI M-OAc)in an MTBS/EMIM weight ratio of 95:5.

After the etching step (step a)), the ABS test plaques were eitherimmersed into a water bath at 50° C. for 10 min (C1) or treated withultrasound (6 L of water, 280 W, corresponding to about 50 W/L, at 35kHz) at 50° C. for 10 min (II).

The SEM images in FIG. 1 show the ABS surfaces which have been obtainedaccording to comparative example C1 (with a simple rinse step) (upperimage) and the ABS surfaces which have been obtained according toinventive example 11 with ultrasound treatment according to theinvention (lower image).

In the SEM images, it is apparent that the ultrasound rinsing step gavemuch better removal of partly dissolved plastic particles which werepartly dissolved by the etch solution. In the SEM image C1 withoutultrasound treatment, voluminous porous plastic residues are clearlyapparent. In the SEM image II with ultrasound treatment, such residuesare entirely absent. The SEM image with ultrasound treatment shows ahomogeneously etched ABS surface having a morphology of particularlygood suitability for conduction of subsequent metallization steps.

EXAMPLE 2 Variation of Etch Conditions

ABS test plaques were treated by the general test method described abovefor examination of etching action.

The etch solution (composition C) used in all cases was a mixture ofmethyltri(1-butyl)ammonium methylsulfate (MTBS),1-ethyl-3-methylimidazolium ethylsulfate (EMI M-EtSO₄) and propylenecarbonate (PC) in an MTBS/EMIM-ETSO₄/PC weight ratio of 80:10:10.Various etch conditions (temperature and time) as described in table 2below were established.

The etching action was checked by means of SEM analysis and shows newstructuring of the surface.

After the etching and rinsing, the test plaques were metallized. Forthis purpose, the following treatment steps were conducted:

-   -   Treatment with activator composition A→treatment with        accelerator composition B→chemical electroless deposition of        nickel using the coating composition M1→electrodeposition of        copper using the coating composition M′.

The following products were used:

-   Activator composition A “Activator U” from HSO or “Surtec 961 Pd”    from Surtec-   Accelerator composition B “HSO Accelerator” from HSO or “Surtec 961    A” from Surtec-   Coating composition M1 “Electroless Nickel 601KB” from HSO or    “Surtec 3/11D” from Surtec-   Coating composition M′ “Copper HD 500” from HSO or “Surtec 867” from    Surtec

The quality of the metal coating is determined with the aid of what iscalled the cross-cut test according to ISO 2409:2007. The results aresummarized in table 1.

TABLE 1 Etch conditions (step a)) Experiment Temperature Treatment timeNo. [° C.] [min] Cross-cut test P1 45 15 inadequate adhesion P2 50 5adhesion P3 50 7 adhesion P4 50 10 adhesion P5 65 5 inadequate adhesionP6 65 7 inadequate adhesion

It is found that, by means of a treatment of the ABS surface in step a)at a temperature of 45° C., even with an etch time of 15 min, it is notpossible to obtain homogeneous structuring of the surface (P1). When theetch temperature is too low and/or the treatment time is too short, thesurface is insufficiently roughened. The nucleation necessary for themetallization in the subsequent step is inadequate. It is not possibleto produce a layer between the plastic surface and metal layers that hasadequate adhesion (insufficient “push-button effect”).

At a higher etch temperature of 65° C. and/or with an excessively longetch time, the plastic surface is attacked excessively (P5 and P6),meaning that the surface is too fissured and exhibits inhomogeneousstructuring.

A particularly advantageous and homogeneous surface structuring of theABS surface was obtained in this example at a temperature in the rangefrom 50 to 60° C., more preferably 50 to 55° C., and with a duration of5 to 15 min (see P2 to P4). In the case of optimal etch parameters, thedepressions (also called caverns) necessary for the “push-button effect”are formed, and the subsequent metal layers have good adhesion. Theoptimal etch conditions, such as time and temperature, may varyaccording to the type of plastic, geometry, injection molding parametersor age of the substrate.

1. A process for coating a plastic surface with at least one metal, theprocess comprising: a) pretreating the plastic surface with acomposition, comprising more than 50% by weight of an ionic liquid,wherein the ionic liquid is a salt which is liquid at 100° C., 1 bar; b)primary treating the plastic surface from a) with an aqueous rinsesolution while applying ultrasound; c) secondary treating the plasticsurface from b) with an activator composition, comprising an ionogenicactivator, a colloidal activator or both of the ionogenic and thecolloidal activator; d) tertiary treating the plastic surface from c)with an accelerator composition, comprising an acid, a reducing agent,or both of the acid and the reducing agent; e) chemically depositing ametal layer, by treating the plastic: surface from d) with a firstcoating composition, comprising a metal salt and a reducing agent; f)electrochemically coating the plastic surface from e) with at least oneadditional metal layer, by electrochemically treating the plasticsurface from step e) with at least one second coating composition,comprising a metal compound. wherein the plastic surface is a plasticcomprising a polyimide, a polystyrene, a copolymer of styrene selectedfrom a styrene/acrylonitrile copolymer, an acrylicester/styrene/acrylonitrile copolymer and anacrylonitrile/butadiene/styrene copolymer, or a mixture thereof and/or amulticomponent plastic comprising the plastic.
 2. (canceled)
 3. Theprocess according to claim 1, wherein the ionic liquid is at least onesalt having a cation selected from the group consisting of animidazolium cation, a pyridinium cation, a pyrazolium cation and analkylammonium cation.
 4. The process according to claim 1, wherein theionic liquid is a salt having an alkylammonium cation of formula (I):

wherein R is an unbranched and unsubstituted C₁-C₁₈-alkyl,CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂— with p=0 to3; R¹, R² and R³ are each independently: a hydrogen atom, unsubstitutedC₁-C₁₈-alkyl, 2-hydroxyethyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl,2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, chlorine,CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)—CH₂CH₂— with p=0 to 3,or two adjacent R¹, R² and R³ radicals together with a nitrogen atom informula (I) form a saturated unsubstituted five- to seven-membered ring;X is an anion; and n is 1, 2 or
 3. 5. The process according to claim 1,wherein the ionic liquid is methyltri(1-butyl)ammonium methylsulfate. 6.The process according to claim 1, wherein the ionic liquid comprises afirst ionic liquid and a second ionic liquid, the first ionic liquidcomprises, as a cation, at least one an alkylammonium cation, and thesecond ionic liquid comprises, as a cation, an aromatic heterocyclehaving a delocalized cationic charge and a nitrogen atom.
 7. The processaccording to claim 1, wherein the ionic liquid is at least one selectedfrom the group consisting of methyltri(1-butyl)ammonium methylsulfate.1-ethyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazoliumethylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium methanesulfonate and1-ethyl-3-methylimidazolium diethylphosphate.
 8. The process accordingto claim 1, wherein the composition comprises 1% to 30% by weight, basedon an overall composition, of at least one solvent selected from thegroup consisting of water, propylene carbonate, polyethylene glycols,diacetin, triacetin, ethylene glycol, diethylene glycol, triethyleneglycol and tetraethylene glycol.
 9. The process according to claim 1,wherein the composition comprises, based on an overall composition: 49%to 94% by weight of a first ionic liquid, which comprises analkylammonium cation; 5% to 50% by weight of a second ionic liquidcomprising, as a cation, an aromatic heterocycle having a delocalizedcationic charge and a nitrogen atom; and 1% to 30% by weight of at leastone solvent selected from the group consisting of water, propylenecarbonate, polyethylene glycols, diacetin, triacetin, ethylene glycol,diethylene triethylene glycol and tetraethylene glycol.
 10. (canceled)11. The process according to claim 1, wherein the metal is at least oneselected from nickel, aluminium, copper, chromium, tin, zinc and analloy thereof.
 12. The process according to claim 1, wherein the plasticsurface is a plastic comprising an acrylonitrile/butadiene/styrenecopolymer, and the pretreating is carried out at a temperature in therange from 50 to 60° C. and over a period of 5 to 15 min.
 13. Theprocess according to claim 1, wherein the prim, treating in b) iscarried out by dipping the plastic surface from a) into an ultrasoundbath comprising the aqueous rinse solution at a power in the range from40 to 60 watts/L, over a period of 1 to 30 min and at a temperature of40 to 60° C., and wherein the aqueous rinse solution comprises at least85% by weigh of water.
 14. The process according to claim 1, wherein b)comprises: b1) treating the plastic surface from a) with a first aqueousrinse solution, by spraying the plastic surface with the first aqueousrinse solution or dipping the plastic surface into the first aqueousrinse solution; and b2) treating the plastic surface from b1) with asecond aqueous rinse solution while applying ultrasound.
 15. The processaccording to claim 1, wherein the electrochemical coating in step f)comprises: f1) electrochemically coating the plastic surface from e)with a layer consisting essentially of copper, nickel, or both of thecopper and the nickel, by treating the plastic surface from e) with athird coating, composition, comprising a copper compound, a nickelcompound, or both of the copper compound and the nickel compound; andf2) electrochemically coating the plastic surface from f1) with a layerconsisting essentially of chromium, by (eating the surface from f1) witha fourth coating composition, comprising a chromium compound.
 16. Theprocess according to claim 1, wherein the plastic surface is a plasticconsisting of a polyamide, a polystyrene, a copolymer of styreneselected from a styrene/acrylonitrile copolymer, an acrylicester/styrene/acrylonitrile copolymer and anacrylonitrile/butadiene/styrene copolymer, or a mixture thereof and/or amulticomponent plastic comprising the plastic.
 17. The process accordingto claim 12, wherein the plastic surface is a plastic consisting of anacrylonitrile/butadiene/styrene copolymer.